Air filter



FIG. 1 is a top perspective view of an air filter according to the present design;

FIG. 2 is a bottom perspective view of the air filter;

FIG. 3 is a top view of the air filter;

FIG. 4 is a bottom view of the air filter; and,

FIG. 5 is a side view of the air filter, the remaining three sides being identical thereto.

The various parts of the air filter shown in broken lines depict environmental subject matter only and form no part of the claimed design. 

CLAIM I claim the ornamental design for an air filter, as shown and described. 